7-5-7

Graphing Paired-Variable Statistical Data

Drawing Quadratic, Cubic, and Quartic Regression Graphs

You can draw a quadratic, cubic, or quartic regression graph based on the plotted points. These graphs use the method of least squares to draw a curve that passes the vicinity of as many data points as possible. These graphs can be expressed as quadratic, cubic, and quartic regression expressions.

The following procedure shows how to graph a quadratic regression only. Graphing the cubic and quartic regressions are similar.

u ClassPad Operation (Quadratic Regression)

Start the graphing operation from the Statistics application’s Graph window or List window.

From the Graph window

Tap [Calc] [Quadratic Reg] [OK] [OK] ".

•For cubic regression tap [Cubic Reg] and for quartic regression tap [Quartic Reg] instead of [Quadratic Reg].

From the List window

Tap [SetGraph][Setting...], or G.

On the Set StatGraphs dialog box that appears, configure a StatGraph setup with the setting shown below, and then tap [Set].

Type: QuadR

•For cubic regression select [CubicR] and for quartic regression tap [QuartR] instead of [QuadR].

Tap yto draw the graph.

The following are the model formulas for each type of regression.

Quadratic Regression

Model Formula: y = a·x2 + b·x + c

a : quadratic regression coefficient

b : linear regression coefficient

c : regression constant term (y-intercept)

r2 : coefficient of determination

MSe : mean square error

 

1

n

• MSe =

Σ (yi – (a·xi 2 + b·xi+ c))2

n – 3

 

i=1

20021201